A high-resolution all-dry resist process is presented that utilizes amorphous zinc-imidazolate (aZnMIm) films deposited by atomic/molecular layer deposition (ALD/MLD), patterned with electron beam lithography (EBL), and developed with a low temperature gas phase etchant, hexafluoroacetylacetone (hfacH), to achieve well-resolved 16nm thick, 20nm pitch lines when using an organic-based underlayer. This work is a continuation of previous efforts that explored deposition, dry development, and pattern transfer. Previously, minimum feature sizes of 29nm thick lines with 40nm pitch were observed, but here, the use of an underlayer was able to shrink critical feature dimensions to 16nm.
With the adoption of extreme ultraviolet lithography (EUVL) to decrease microelectronic device dimensions, recent photoresist research has focused on the development of next generation metal-organic resist materials. To enhance lithographic capabilities and mitigate common drawbacks seen from traditional solvent based processes like spin coating and solution phase development, interest has shifted towards solvent-free “dry” deposition and development. These dry techniques can obviate extra processing steps, significantly reduce the amount of solvent waste generated, and even allow for reduced defect density and higher resolution. The process described herein avoids the use of solvents, and ultimately many issues associated with solvents, by depositing metal-organic resists using atomic/molecular layer deposition (ALD/MLD) and developing them using a selective thermal dry etching process. The low temperature (e.g., 100-120°C) thermal development conditions used in this study are notable in the context of lithography processes, as the high temperatures required in other dry etching processes can be difficult to implement in nanofabrication processes. Our previous work has focused on using amorphous zinc-imidazolate (aZnMIm) films in an all-dry resist technology, achieving resolution down to 22nm. Here, we explore the role of temperature and time on dry development and examine pattern transfer into silicon substrates. Preliminary pattern transfer experiments suggest that an etch selectivity of at least 7:1 exists for electron-beam treated aZnMIm over silicon using a pseudo-Bosch plasma etch. Our findings demonstrate the feasibility of dry development at lower temperatures and times and suggest potential for aZnMIm as a high-resolution resist for nextgeneration lithography.
We report on the continuous wave (CW) room temperature operation of epitaxially regrown monolithic GaSb-based photonic crystal surface emitting diode lasers (PCSEL) with λ ≈ 2 μm. The devices are based on laser heterostructure containing carrier stopper layer designed to inhibit electron leakage into buried photonic-crystal section. Atomic hydrogen cleaning of the nanopatterned surface followed by optimized epitaxial step resulted in highly uniform airpocket-retaining regrowth. The increase of the number of air-pockets in unit cells of the buried photonic crystal layer led to enhancement of the PCSEL output power and improvement of the far field pattern The PCSELs with buried high-index-contrast photonic crystal utilizing four air-pockets per unit cell generated 30 mW of continuous wave power from 200 μm diameter aperture.
Polymer blending is a powerful approach to expand the nanopatterning landscape for block copolymer (BCP) directed self-assembly, itself a promising route to enhance resolution in established lithography techniques. However, investigating the vast and complex parameter spaces associated with blend self-assembly remains a daunting challenge. This talk will highlight examples where blending BCPs with homopolymers can dramatically speed up self-assembly kinetics for potential applications from nanophotonics to membrane synthesis, while blending two BCPs enables registered, template-responsive pattern selection. I will further describe ongoing efforts to accelerate investigations of blend formulation and processing using new combinatorial and autonomous methods.
Infiltration synthesis of vapor-phase precursors is ex-situ route of converting established polymeric resists into hybrids. The concept initially modelled over polymethylmethacrylate (PMMA)-AlOx hybrid has been expanded to infiltrating several metal oxide moieties into high sensitivity resist (HSR). Beyond implementing single metal oxide species, alloyed infiltration is explored as a means to limit pattern roughness originating from granular crystallites. Lithography performance of these new generation of hybrid positive tone resists is assessed towards contact-hole patterning.
High-NA EUV lithography required for continued extreme downscaling of Si devices demands ultrathin photoresists with high EUV patterning performance and etch resistance. This talk briefs our current efforts on synthesizing new organic-inorganic hybrid resists based on atomic layer deposition (ALD) techniques and characterizing their electron beam and EUV patterning characteristics. Two distinctive approaches are discussed–vapor-phase infiltration (VPI) and molecular ALD (MALD), where the former utilizes an infiltration of gaseous inorganic precursors into existing organic resists and the latter a cyclic layering of organic and inorganic moieties. Featured systems include an indium-oxide-infiltrated PMMA and a MALD hybrid resist comprising trimethylaluminum (TMA) and hydroquinone (HQ). Given the facile implementablility and control of resist composition and characteristics, the ALD-based hybrid resist synthesis has a potential for enabling high-performance EUV photoresist systems.
High-NA EUV lithography–scheduled to be implemented in a few years for high-volume manufacturing of extremely downscaled Si devices with 2 nm node and beyond–demands ultrathin organic-inorganic hybrid photoresists with high EUV sensitivity and etch resistance. In this work, we synthesized a positive-tone hybrid photoresist composed of PMMA infiltrated with molecular network of indium oxide by vapor-phase infiltration (VPI), an ex-situ inorganic hybridization method derived from atomic layer deposition, and evaluated its patterning characteristics by electron-beam and EUV lithography (EBL and EUVL). The hybrid resist featured significantly enhanced etch resistance under dry etching but also the critical doses of 300 uC/cm2 for EBL and 60 mJ/cm2 for EUVL, both largely comparable to those of PMMA. Unlike alumina infiltration in PMMA that has been demonstrated previously, it was found that the weak binding nature of trimethyl indium (TMIn), the gaseous precursor used to infiltrate indium oxide in PMMA matrix, to the carbonyl group in PMMA enabled a uniform distribution of the oxide content across the PMMA thickness. However, it also led to undesired residue in the developed regions due to the strong interaction between the Lewis-basic hydroxyl groups on the surface of starting Si substrate with infiltrated TMIn. The residue issue could be mitigated by passivating the Si surface by hexamethyldisilizane (HMDS) and combining the acid/base rinse and oxygen plasma descum. The results not only hint at the potential of VPI-based ex-situ hybridization in developing novel hybrid EUV photoresists but also highlight the technological details that must be addressed to enable high EUVL performance in the infiltrated hybrid resist system.
Infiltration synthesis is an emerging material hybridization technique. Starting with a brief dive into infiltration synthesis mechanism, I will present our pioneering work on ex-situ conversion of conventional organic photoresists into hybrid EUV resists as well as the generation of mechanically resilient hybrids with one of the highest storage elastic strain energy capacities for potential applications in MEMS technologies. I will also overview the use of infiltration synthesis approach for hybridizing nanopatterned polymer templates and self-assembled block copolymer thin films to form robust dry etch masks for pattern transfer as well as direct-writing oxide nanostructures for optoelectronic device applications.
Photonic crystal surface emitting lasers emitting up to 2.6 µm have been designed and fabricated. A high-index-contrast photonic crystal layer was incorporated into the laser heterostructure by air-hole-retaining epitaxial regrowth. Transmission electron microscopy studies demonstrated uniform and continuous regrowth of the nano-patterned GaSb surface with AlGaAsSb alloy until air-pockets start being formed. The photonic crystal surface emitting lasers based on diode laser and cascade diode laser heterostructures generated narrow spectrum low divergence beams with mW-level output power. The angle-resolved electroluminescence analysis demonstrated well resolved photonic subbands corresponding to Γ2 point of square lattice and photonic gaps of several meV.
Improvements in ordering kinetics and pattern diversity are needed to make block copolymer directed self-assembly (BCP DSA) a route to cost-effective, large-area nanomanufacturing. This talk will highlight recent research in BCP DSA with these goals in mind. First, I will describe how self-templating in layered BCP thin films produces new 3D pattern symmetries. Second I will show how chemical patterning can be used to locally select between coexisting cylinder and lamellae morphologies in BCP blends. Finally, I will discuss the use of homopolymer plasticizers to accelerate ordering, enabling self-assembly at the > ~100 nm scale relevant for optical dielectric metasurfaces.
We have developed an organic-inorganic hybrid resist platform featuring versatile ex-situ control of its performance by incorporating inorganic elements using vapor-phase infiltration (VPI) into standard organic resists. With poly(methyl methacrylate) (PMMA)-AlOx hybrid as a model composition we unveiled controllability of the critical exposure dose, contrast (as high as ~30), and etch resistance; estimated Si etch selectivity over ~300, demonstrating high aspect ratio ~17 with ~30 nm resolution Si fin-structures. Building upon the demonstration of PMMA-AlOx hybrid resist, we expanded our material portfolio to a high sensitivity resist and other inorganic moieties. We present preliminary results obtained from the extreme ultraviolet (EUV) lithography dose tests conducted on corresponding infiltrated hybrids and optimization of infiltration with the help of transmission electron microscopy (TEM).
We demonstrate a simple ex-situ inorganic infiltration route for transforming standard organic resists into high-performance positive tone hybrid resist platform. A model thin film PMMA-AlOx hybrid resist system has been synthesized by hybridization of PMMA with AlOx and investigated for electron beam lithography. The approach possesses full controllability of the resist performance in terms of critical does, patterning contrast reaching up to 30 and etch resistance for plasma-based pattern transfer processes. The high selectivity Si etching capability demonstrated using a low-temperature cryo-Si etch process, based on the controlled infiltration outperforms commercial resists and typical hard mask material thermal SiO2, with estimated achievable selectivity in excess of ~300. Si nanostructures down to ~30 nm with aspect ratio up to ~17 are also transferred into the Si substrate. Easy implementation and adaptability for different inorganic infiltrations, this platform is well capable of potentially delivering the resist performance and throughput necessary for EUV lithography.
We report on development of the mid-infrared antimonide based laser technology targeting dual wavelength operation for intra-cavity difference frequency generation. The devices utilize Y-branch architecture with high order DBR reflectors controlling the laser emission spectrum. The device active region contain asymmetric tunnel coupled quantum well with built in resonant second order nonlinearity. The epitaxially regrown photonic crystal surface emitting GaSb-based lasers will be demonstrated.
The external cavity tunable mid-infrared emitters based on Littrow configuration and utilizing three stages type-I quantum well cascade diode laser gain elements were designed and fabricated. The free-standing coated 7.5-μm-wide ridge waveguide lasers generated more than 30 mW of continuous wave power near 3.25 μm at 20°C when mounted epi-side-up on copper blocks. The external cavity lasers (ECLs) utilized 2-mm-long gain chips with straight ridge design and anti-/neutral-reflection coated facets. The ECLs demonstrated narrow spectrum tunable operation with several milliwatts of output power in spectral region from 3.05 to 3.25 μm corresponding to ∼25 meV of tuning range.
Sophie Morley, Aaron Stein, Mark Rosamond, Diego Alba Venero, Aleš Hrabec, Philippa Shepley, Mi-Young Im, Peter Fischer, Matthew Bryan, Dan Allwood, Paul Steadman, Sean Langridge, Christopher Marrows
Artificial spin ices are often spoken of as being realisations of some of the celebrated vertex models of statistical mechanics, where the exact microstate of the system can be imaged using advanced magnetic microscopy methods. The fact that a stable image can be formed means that the system is in fact athermal and not undergoing the usual finite-temperature fluctuations of a statistical mechanical system. In this paper we report on the preparation of artificial spin ices with islands that are thermally fluctuating due to their very small size. The relaxation rate of these islands was determined using variable frequency focused magneto-optic Kerr measurements. We performed magnetic imaging of artificial spin ice under varied temperature and magnetic field using X-ray transmission microscopy which uses X-ray magnetic circular dichroism to generate magnetic contrast. We have developed an on-membrane heater in order to apply temperatures in excess of 700 K and have shown increased dynamics due to higher temperature. Due to the ‘photon-in, photon-out' method employed here, it is the first report where it is possible to image the microstates of an ASI system under the simultaneous application of temperature and magnetic field, enabling the determination of relaxation rates, coercivties, and the analysis of vertex population during reversal.
High-energy x-rays from a synchrotron source are well suited for numerous applications, such as studies of
materials structure and stress in bulk or extreme environments. Some of these methods require high spatial
resolution. Planar kinoforms are shown to focus monochromatized undulator radiation in the 50–100 keV
range down to 0.2–1.5 μm beam sizes at 0.25–2 m focal distances. These lenses were fabricated by reactive ion
etching of silicon. At such high x-ray energies, these optics can offer substantial transmission and lens aperture.
A table top nanofabrication system which combines the classic Talbot imaging effect and a compact table top soft-x ray
laser is described in this paper. Periodic nanostructures on millimeter square are fabricated using this robust, simple and
defect tolerant fabrication method. Talbot lithography allows for a complete coherent extreme ultraviolet lithography
process in a compact table top system. Double exposure allowed for the reduction of the feature sizes.
We describe a table top nanofabrication system that utilizes the coherent Talbot imaging effect and a table-top soft x ray laser to implement a defect-free compact nanolithography tool. The Talbot lithography provides a robust and simple setup capable of printing periodic structures over millimeter square areas free of defects. Test structures were fabricated into metal layers showing a complete coherent extreme ultraviolet lithographic process in a table-top system.
We have evaluated the applicability of vertically-focusing kinoform lenses for tailoring the vertical coherence
length of storage-ring undulator x-ray beams so that the entirety of the coherent flux can be used for small
angle multi-speckle x-ray photon correlation spectroscopy (XPCS) experiments. We find that the focused beam
produced by a kinoform lens preserves the coherence of the incident unfocused beam and that at an appropriate
distance downstream of the focus, the diverging beam produces speckles nearly identical to those produced by
an equivalently-sized unfocused beam. We have also investigated the effect of imperfect beamline optics on the
observed coherence properties of the beam. Via phase contrast imaging and beam-divergence measurements,
we find that a horizontally-deflecting mirror in our beamline precludes us from seeing the true radiation source
point but instead acts as an apparent source of fixed size at the center of our insertion device straight section.
Finally, we discuss how expected near-future optimization of these optics will greatly benefit XPCS measurements
performed at beamline 8-ID-I at the Advanced Photon Source.
While hard x-rays have wavelengths in the nanometer and sub-nanometer range, the ability to focus them is limited by the quality of sources and optics, and not by the wavelength. A few options, including reflective (mirrors), diffractive (zone plates) and refractive (CRL's) are available, each with their own limitations. Here we present our work with kinoform lenses which are refractive lenses with all material causing redundant 2π phase shifts removed to reduce the absorption problems inherently limiting the resolution of refractive lenses. By stacking kinoform lenses together, the effective numerical aperture, and thus the focusing resolution, can be increased. The present status of kinoform lens fabrication and testing at Brookhaven is presented as well as future plans toward achieving nanometer resolution.
This paper describes the use of a unique combination of an environmentally stable chemically amplified photoresist (UV113, Shipley) and a copolymer of methyl styrene and chloromethyl acrylate P(MS/CMA) resist (ZEP520, Zeon), without any additional intermediate layers, in the fabrication of micro- and nanochannels. The two resists used are innocuous to each other during the designed process flow, providing flexibility, high resolution, greater throughput and ease of use. We have also determined that the maximum channel length is limited by diffusion and mass transport effects, and that sub-100 nm nanochannels can be obtained with 30 micron lengths.
To image weakly absorbing materials (e.g. biological specimens, thin films, etc.) with hard x-ray photons, phase-contrast methods have to be applied to enhance the image contrast. Micro-fabricated Fresnel prisms in silicon have been manufactured to enable wavefront division of the incoming x-ray beam for phase-contrast applications. To maximize the efficiency and aperture of these optics, multiples of 2π phase-shifting regions in a conventional prism structure have been deleted, leading to structures that are arrays of micro-prisms. We show preliminary results of x-ray beam deflection using a variety of micro-prism arrays at the NSLS X13B undulator beamline at 11.3 keV.
Kinoform lenses avoid the absorption losses from a comparable refractive lens by removing all material causing redundant 2π phase shifts. Such optics allow high resolution imaging with a theoretical 94% focusing efficiency. While fabrication of kinoform lenses for two-dimensional focusing is difficult, standard lithographic processes can be utilized to fabricate optics in silicon which produce a line focus. By putting two single-dimension kinoform lenses in a crossed-pair arrangement, a two-dimensional spot is achieved. First attempts at imaging with a crossed pair of kinoform lenses are presented.
One application of Kinoform Fresnel Lenses is to generate small focal spots of hard X-ray photons with high gain for micro-diffraction experiments. A Kinoform lens can be obtained from a refractive lens by deleting material such that at the design photon energy, the deleted regions correspond to with modulo 2π phase-shifts in the phase front. At photon energies different from the design photon energy, the phase jumps are no longer 2π, and the diffractive properties of the kinoform become more significant. We present measurements and calculations of spot size versus photon energy.
Soft x-ray scanning transmission x-ray microscopy allows one to image dry and wet environmental science, biological, polymer, and geochemical specimens on a nanoscale. Recent advances in instrumentation at the X-1A beamline at the National Synchrotron Light Source at Brookhaven National Laboratory are described. Recent results on Nomarski differential phase contrast and first results on investigations at the oxygen K edge and iron L edge of hydrous ferric oxide transformations are presented.
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